1. Field of the Invention
The present invention relates to a probe scanning method for a scanning probe microscope, and more particularly relates to a probe scanning method for an atomic force microscope using a force acting on a cantilever probe and a sample and for a scanning tunneling microscope using a tunnel current flowing between a probe and a sample.
2. Description of the Prior Art
The scanning probe microscope principally uses physical quantities acting on a probe and a sample when the former comes near the latter. Such a microscope is one of the new microscopes designed in order to observe physical quantities of a sample surface by measuring effects of the physical quantities acting on the probe.
The atomic force microscope or the scanning tunneling microscope is a kind of scanning probe microscope. The atomic force microscope uses an atomic force acting on a cantilever probe and a sample in order to control a distance between the probe and the sample, and measures physical quantities acting on them. The scanning tunneling microscope uses a tunnel current flowing between a conductive probe and a sample in order to control a distance between the probe and the sample, and measures physical quantities acting on them.
With the scanning probe microscope, the distance between the probe and the sample is controlled to be constant, a micro mechanism, such as a piezoelectric device, raster scans the sample surface, and quantities of control exerted by the micro mechanism are expressed by images, so that a shape or physical quantities of the sample surface can be observed.
The raster scan method which is a typical relative scanning method applied to the probe and sample will be described with reference to FIG. 3.
In the conventional raster scan method, the probe is relatively moved in the X direction with respect to the sample. Physical quantities acting on the probe and sample are measured each time the probe is moved in the X direction by +1 scanning unit. The measured physical quantities constitute one-picture-element data denoting a position of the probe and sample. When data of physical quantities are measured and collected for all the scanning units, the probe is moved by +1 scanning unit in the Y direction, and is positioned at the coordinate 0 in the X direction. The foregoing movements are repeated in order to measure the physical quantities acting on the surfaces of the probe and sample.
With the scanning probe microscope, physical quantities acting on the probe and sample are usually measured by precisely controlling the distance between them to several nm or less. When measuring the physical quantities acting on the probe and sample, the compatibility of high resolution and high speed measurement is subject to a certain limit, which is a problem in view of throughput improvement. This problem is particularly serious if a sample surface is uneven by approximately several 100 nm or more. In such a case, the probe and sample may be damaged if they crash against each other. Therefore, it is impossible to easily accelerate the scanning operation.
In the raster scan method of FIG. 3, it is necessary to increase the number of scanning units in the X and Y directions when performing the measurement with high resolution. However, throughput of the measurement is inversely proportional to the number of scanning units in the Y direction. In other words, if it takes time t to scan one line in the X direction, total time for scanning the sample surface is tX (i.e. the number of scanning units in the Y direction). The more scanning units there are in the Y direction, the longer the measurement time. Further, in order to accelerate the measurement, the number of scanning units in the Y direction has to be reduced, which means reduced resolution.
The invention is intended to overcome the foregoing problems of the related art, and provides a method which can not only maintain high resolution, but can also accelerate a scanning operation in order to reduce overall measuring time.
As described above, it is principally difficult for the conventional scanning probe microscope using the raster scan technique shown in FIG. 3 to perform the measurement with high resolution and at a high speed. According to the invention, when moving in a main scanning direction from a position 1 to a position 2 as shown in FIG. 3, a probe is staggered or scanned in a zigzag pattern relative to a sample in the X and Y directions (refer to FIGS. 1 and 2) in order to measure physical quantities acting on the probe and the sample.
In accordance with the scanning method shown in FIG. 1, the relative moving speed of the probe on an uneven surface of the sample is substantially equal to that of the raster scan method of FIG. 3. However, areas to be measured can be approximately doubled, which means substantial improvement in a scanning speed.